Sea cucumbers, related to sea stars and sea urchins, look a lot like garden slugs, the nemesis of gardeners everywhere. They’re squishy, plump, and often spiny (hence the name), and without some knowledge of sea cucumber anatomy, the layperson is unlikely to know its head from its tail.
That’s unfortunate because the tail end of the sea cucumber means business. In addition to being responsible for excretion (common for the tail end of most animals), the anus of the sea cucumber is also responsible for respiration—it literally holds its breath by clenching its butt.
And that’s not even the most interesting thing about the sea cucumber’s anus: It’s also responsible for some very unique defensive capabilities, which vary across the more than 1,200 species.
First, when threatened, the sea cucumber excretes a type of saponin called holothurin that is toxic to many species of fish—though, curiously, not the pearlfish, which is protected by a thick layer of mucous, and likes to burrow into the sea cucumber’s anus when it opens its orifice to breathe and set up house there. Most other sea creatures, however, find the toxin very dangerous. In addition to fending off predators, the saponins are also thought to protect sea cucumbers from harmful pathogens and fungi, which is the same role these compounds play in plants.
Some species of sea cucumber dial up their defenses a notch by shooting an organ called Cuvierian tubules out of the anus when threatened. These extremely sticky threads stun and confuse predators. Other species take it one step farther by shooting their internal organs out of the same orifice to ensnare predators in a process known as auto-evisceration. The sea cucumber literally spills its guts, and remarkably, lives to tell the tale. Those organs regenerate within a few weeks by essentially reprogramming specialized cells for a different purpose—a process called dedifferentiation that is of great interest to biologists, who would love to learn how to regenerate tissue in humans by similar means. A stellar example of nature’s dual-use technologies.
Such myriad defense mechanisms are necessary for biologically simple slow-moving sea creatures with little external armor. How much more multifaceted must the security mechanisms be for more complex organisms, like mammals? Humans, in particular?
You all live in 2024, so you know the answer: It’s exponential. The threats are physical, biological, cyber, territorial, and even existential. And for every threat, there is at least one hero, and often hundreds or thousands, who are working to stop it. Many of those heroes wear camo fatigues, but a great many wear lab coats.
This issue of Photonics Focus is dedicated to the security of infrastructure, national borders, and technology networks. Feature articles explore topics like high-energy laser weapons and geospatial intelligence, which fuses satellite imagery with open-source data, social media, and AI to gather crucial real-time information. And, in a fun romp through the CIA’s invite-only museum, Photonics Focus managing editor William Schulz takes us on a tour of the optics of Cold War espionage.
Time and again, optics and photonics contribute to the myriad tools that protect, safeguard, and defend. And, like the unique dedifferentiating cells of the sea cucumber, many of these technologies that were originally designed for defense are ultimately repurposed for life-changing civilian uses. Enjoy.
Gwen Weerts, Editor-in-chief
